Well I broke down and decided to clean my sensor on my MArk IIN.
While it seems traumatic, it turned out to be no big deal. I had done this before, but found myself far to conservative in the pressure I used when cleaning it the first time. You can't just let the pressure of the wand do the work. Reading the instructions 3 or 4 dozen times, I finally decided to believe that you have to use the pressure of writing with a pencil. No guts, no glory.
Rocket Blower moved the dust around effectively:
First cleaning (the instructions suggested it might take 2 or 3 passes with different pec pads for stubborn dust):
That was good enough, but I couldn't leave well enough alone. One more rocket blower blast:
Another blower blast and I stopped being fanatical:
I'm sure I could have swabbed a third time and taken a spec or two off, but I decided moving the spec around was enough trauma for now.